Muffled exhaust release for an outboard motor



July 24, 1962 R. P. HULSEBUS 3,045,423

MUFFLED EXHAUST RELEASE FOR AN OUTBOARD MOTOR Filed Sept. 23, 1958INVENTOR. Z/cmwep P. HULSEBUJ nited rates atent 3,945,423 Patented July24, 1962 fiice I 3,045,423 MUFFLED EXHAUST RELEASE FOR AN OUTBOARD MOTORRichard P. Hulsebus, Waukegan, Ill., assignor to Outboard MarineCorporation, Waukegan, [1]., a corporation of Delaware Filed Sept. 23,1958, Ser. No. 762,744 6 Claims. (CI. 60-32) This invention relates to amufiied exhaust release for an outboard motor.

It is an object of the invention to provide an alternate passage for theexhaust gases when the motor is operating at low speeds and the normalexhaust passage is blocked by the water through which the motor istraveling, without releasing the motor noises as such relief passageshave done in the past. With that object in mind my outboard motor isprovided with an exhaust tube extending downwardly from the exhaustmanifold of the engine to a first expansion chamber in the lower unit,tubular passages from the first expansion chamber to a second expansionchamber, and a passage from the second expansion chamber to the outsideair which includes a flexible tube to isolate the vibration of theexpansion chamber from the motor housing. The first expansion chamberhas the usual outlet below the water line, from which the water isdrained at moderate to high speed by reduction of pressure due to themovement of the motor through the water. The entire system is designedfor a minimum of back pressure on the exhaust port of the engine and amaximum of mufiling action at low speeds.

The drawing is a side elevational view of an outboard motor, withportions of the motor housing and lower unit broken away to show theexhaust system which comprises my invention.

The drawing shows an outboard motor having a motor housing 10 which notonly covers the engine, but is continuous over the lower unit 11 to thewater line 12, thus providing a sound barrier between the engine and theoccupants of the boat. The cylinders of the engine are provided withexhaust ports 13 which open into an exhaust manifold 14. At the lowerside of the exhaust manifold an exhaust tube 15 is secured to themanifold, extending downwardly into the lower unit 11. The lower unit 11 is provided with a bafiie -16 between the ends of the exhaust tube 15,and a resilient gasket 17 is provided between bafiie 16 and exhaust tube15. -A shoulder 18 on the exhaust tube compresses gasket 17' againstbaffle 16, to seal the first, or lower expansion chamber 19 from thesecond, or upper, expansion chamber 20, and at the same time to preventthe transmission of vibrations from the exhaust tube to the lower unit11.

Short tubes 21 extend from the lower, or first, expansion chamber to theupper, or second, expansion chamber. From the second expansion chamber ashort tube 22 extends outwardly toward the motor cover 10, which isprovided with a tapered opening 23 aligned with tube 22 and extending tothe outside air. A corrugated flexible hose 24 is slipped over the tube22, and is provided with a tapered end portion 25 which engages thetapered opening 23 in motor housing 10. -A spring 26 is seated on theend of tube 22 at one end and the other end seats on the tapered end oftube 24. Thus tube 24 is engaged firmly in tapered seat 23 regardless ofthe vibration of lower unit 11 with respect to motor cover 10.

The lower portion of first expansion chamber 19 is provided with anexhaust outlet 30 well below the water line and a passage 31 connectingthe chamber 19- with the outlet 30, said passage 31 being inclinedrearwardly with respect to the norm-a1 direction of travel so that whenthe motor attains a moderate speed through the water, the water inpassage 31 will be drawn out of outlet 30, creating an area of loweredpressure which permits the exhaust to be discharged through outlet 30 inthe conventional manner. The noise of the exhaust is thus dissipated inthe water when the motor is moving at sufiicient speed. At lower speedsthe water will not be drawn out of passage 31, and will block it, butthe exhaust passes upwardly through tubes 21 in baffle 16 to the secondexpansion chamber 20 and thence through tubes 22 and 24 to the outsideair. The length of the tubes 21 may be chosen to conflict with the wavelength of the sound waves, greatly impeding the transmission of soundthrough baffle 16, and tube 15 may likewise be of a length to impedepropagation of the sound waves. In general, an open tube having a lengthwhich is not a multiple of one-half of the wave length of the soundpassing through it will prevent the formation of standing waves and willinterfere with propagation of the sound waves. This length is determinedby the sounds which are produced by the motor at low speeds, when theexhaust is discharged into the air through tube 24. The successiveexpansion chambers 19 and 20 will attenuate the sound because of theirlarge volumes in comparison with that of the exhaust tube.

A resilient gasket 32 is provided between lower unit 11 and motor cover1'2 to further isolate the sound waves and vibration in lower unit 11from motor cover 12 while maintaining the motor cover in its properrelative position. Gasket 32 is restrained from axial movement byshoulders 33 on lower unit 11.

The space between the motor cover 10 and the lower unit 11 is a dead airspace 40 which isolates the exhaust system, since it completelysurrounds the lower unit and is closed at the bottom, as shown by waterline 12, and divided in the middle by gasket 32. Bellows tube 24prevents transmission of vibrations across space 40.

The upper portion of the motor housing or cover 10 is secured to theengine supports in the manner shown in Irgens Patent 2,740,368, so thatthe cover is completely isolated by resilient members from the engineand other moving parts which produce vibration. Unlike the device of theIrgens patent, the lower resilient mem bers are a part of the exhaustsilencing system, as outlined above. If desired, additional resilientmembers may be interposed between the motor cover and the transombracket and associated vertical pivot, as shown in Irgens.

The transom bracket 41 and its associated parts are secured to motorcover 10, whether or not resilient members are interposed. Since themotor cover is isolated from vibration, the vibrations are nottransmitted to the boat, which is thus prevented from acting as asounding board to amplify the sound as has been the case in the past.

Other arrangements of the first and second expansion chambers arepossible within the scope of my invention. It is also possible toarrange space 40 so that it is not fully closed, or omit it, withoutimparing the improvement in mufliing attained by the exhaust systemitself.

Anexpansion chamberwithin the meaning of the present application isdefined as a chamber having at least two dimensions which are materiallygreater than the largest dimension of the exhaust pipe in any directiontransverse to the flow of exhaust gas therein.

I claim:

1. In an outboard propulsion device, the combination of,

a lower unit designed to operate partially submerged in water,

an engine mounted above said unit,

3 an exhaust gas conduit leading from said engine into said lower unit,

means in said lower unit defining a first expansion chamber connectedwith said conduit, having a materially larger cross section than saidconduit in the direction of How of exhaust gases through said conduit,and having an outlet which is under water when the propulsion device isin use and from which exhaust gas is aspirated when said unit is inmotion,

means in said lower unit defining a second expansion chamber,

means affording direct communication between said first expansionchamber and said second expansion chamber and having a materiallysmaller cross section than said second expansion chamber in thedirection of flow of said exhaust gases therethrough, said secondchamber having communication with said conduit solely through said firstexpansion chamber and said last mentioned means, and

permanently open means for discharging exhaust gases from the secondexhaust chamber at a point above the normal water level after theexhaust gas has passed successively through said conduit, said firstchamber, and said second chamber.

2. An outboard propulsion device according to claim 1 in which in whichthe means providing communication from the first mentioned chamber tothe second expansion chamber comprises at least one tube of substantiallength and difiering materially from any multiple of one half of thewave length of sound waves produced in exhaust gases at low enginespeed.

4. An outboard propulsion device according to claim 1 in which saidsecond expansion chamber is located above the first expansion chamberand is separated therefrom by a transverse partition,

said exhaust gas conduit comprises a tube of substantial lengthdiffering materially from any multiple of one half the Wave length ofsound waves produced at low engine speed in the exhaust gases traversingthe tube,

said tube being fixed to the engine and extending through said partitionand having elastic packing extending about the tube between it and thepartition,

the means aifording communication between the first expansion chamberand the second expansion chamber comprising a short tubular port in saidpartition.

5. An outboard propulsion device according to claim 1 further includingan engine cover having a portion extending downwardly about said lowerunit toward the level of the water in which said unit is operable inuse,

means providing elastic spacing between the lower unit and the enginecover, and

said permanently open means for discharging exhaust gas from said secondchamber being partially enclosed by said engine cover portion wherebythe exhaust gas from said second chamber passes through said coverportion.

6. An outboard propulsion device according to claim 1 and furtherincluding a flexible hose having one end connected with the said lowerunit about the said permanently open means and having its other endconnected with said downwardly extending engine cover portion, the saidportion having an open port above water level through which said hoseopens in communication with the atmosphere.

References Cited in the file of this patent UNITED STATES PATENTS

